IV DRUG ADMINISTRATION
Drug Calculations
November 2007
Drug Calculation Assessment
SECTION 1: Units & Equivalences
SECTION 2: Calculating dose as volume
SECTION 3: Drug Strengths & Stated Concentrations
SECTION 4: Duration of Infusion – Stated rate (dose per min) & Infusion rate (mL/hr)
SECTION 5: Infusion Rate Calculations
SECTION 1:
Units & Equivalences
1 Kg =
1,000 g
1 g =
1,000 mg
1 mg =
1,000 micrograms
1 L =
1,000 mL
Converting from One Unit to Another
To convert from a larger unit to a smaller unit, multiply by 1000 or move the decimal point three places to the right
To convert from a smaller unit to a larger unit, divide by 1000 or move the decimal point three places to the left
Units & Equivalences
Convert 0.25 mg into micrograms
Convert 600 micrograms to mg
Answers
0.25 × 1000 or move decimal point three places to the RIGHT
= 250 micrograms
600 ÷ 1000 or move the decimal point three places to the LEFT
= 0.6 mg
SECTION 2: Calculating Dose as Volume
What you WANT X what it is IN
What you have GOT
= the volume you want to administer
What we WANT
Furosemide 250mg/10mL
Furosemide
Time
0700-0900
1200-1400
Dose
200mg
Route
IV
Start Date
18.05.07
End Date
1600-1800
2200-2400
Other Time
Signature of Doctor
P.Rescriber
What we have GOT
What it is IN
A patient is prescribed 200mg of Furosemide I.V. The ampoules available contain 250mg in 10mL. What volume containing the drug do you need to administer?
Answer
What you WANT X what it is IN
What you have GOT
200 mg
250 mg × 10 mL
= 8 mL
SECTION 3: Drug Strengths & Stated Concentrations
What you HAVE (mg)
CONCENTRATION (mg/mL)
= How much fluid is required (Volume)
Aciclovir
Time
0700-0900
1200-1400
Dose
250mg
Route
IV
Start Date
18.05.07
End Date
1600-1800
2200-2400
Other Time
Signature of Doctor
Additional Comments
P.Rescriber
Final Concentration 5mg/mL
A patient is prescribed 250mg of Aciclovir I.V. Aciclovir has to be initially reconstituted with water for injection, then added to a bag of compatible infusion fluid, giving a final concentration of 5mg/mL. How much infusion fluid should be used dilute the reconstituted Aciclovir to achieve this final concentration?
What we HAVE
CONCENTRATION
Answer
What you HAVE (mg)
CONCENTRATION (mg/mL)
250mg
5mg/mL
= 50 mL
A 1% (w/v) solution means that in every 100mL of solution you will find 1g of drug. Therefore, how many g of Glucose would there be in 500mL of 5% Glucose?
Glucose 5%
500ml
Answer
A 1% (w/v) solution means that in every 100mL of solution you will find 1g of drug.
100mL = 1g
Therefore a 5% w/v must mean that
100mL = 5g
Multiply each side by 5
500mL = 25g
1:10,000 strength means that in every 10,000ml of solution you will find 1g of Adrenaline. Therefore, how many mg of Adrenaline would there be in 10mL of 1:10,000 Adrenaline?
Answer
1:10,000 means that 1g of adrenaline is dissolved in 10,000mL.
1g = 10,000mL
1000mg = 10,000mL
Divide both sides by 1000
1mg = 10mL
SECTION 4: Duration of Infusion
Stated rate (dose per min)
Infusion rate (mL/hr)
Stated Rate – dose per min
Dose (mg) = Time
Rate (mg/min)
Furosemide must be administered at a rate no faster than 4mg/minute. How many minutes would it take to give 200mg of this drug?
Furosemide
Time
0700-0900
1200-1400
Dose
200mg
Route
IV
Start Date
18.05.07
End Date
1600-1800
2200-2400
Other Time
Signature of Doctor
Additional Comments
P.Rescriber
Rate of 4mg/minute
Furosemide 250mg/10mL
Rate
(mg/min)
DOSE(mg)
Answer
Dose (mg) = Time
Rate (mg/min)
200mg
4mg/min
= 50 minutes
Infusion rate – mL/hr
Volume (mL) = Rate (mL/min)
Time (Min)
X 60 = Rate (mL/Hr)
* Tip if rate is in hours omit “X 60”
Omeprazole 40mg/100mL
Omeprazole (Losec ®) 40mg is diluted in 100mL of compatible infusion fluid. This infusion has to be given over 20 minutes. What rate should you set the infusion pump at, in ml/hr, to deliver this dose?
Answer
Volume (mL) = Time (mL/hr) x 60
Rate (hr)
100ml
20 mins x 60
= 300mL/hr
Acetylcysteine 7.5g/1000mL
Acetylcysteine (Parvolex ®) 7.5g is diluted in 1000mL of compatible infusion fluid. This infusion has to be given over 16 hours. What rate should you set the infusion pump at, in ml/hr, to deliver this dose?
Answer
Dose (mL) = Time (mL/hr)
Rate (hr)
1000
16
= 62.5 mL/hr
SECTION 5: Infusion Rate Calculations
What you WANT x 60 (60 mins per hr)
What you have GOT X what it is IN
= the volume you want to administer
Glyceryl Trinitrate
Time
0700-0900
1200-1400
Dose
25 micrograms/
minute
Route
IV
Start Date
18.05.07
End Date
1600-1800
2200-2400
Other Time
Signature of Doctor
Additional Comments
P.Rescriber
Continuous Infusion
You are required to give a patient Glyceryl Trinitrate as a continuous I.V infusion at 25 micrograms/minute. You have prepared a 50mg in 50mL infusion. What rate should you set the infusion pump at, in ml/hr, to deliver this dose?
What we WANT
Glyceryl Trinitrate 50mg/50mL
What we have GOT
What its IN
60 mins per hr
Answer
What you WANT x 60 (60 mins per hr)
What you have GOT X what it is IN
25 micrograms x 60 = 1500 micrograms/hr
1500 ÷ 1000
= 1.5 mg
1.5 mg x 50mL
50 mg
= 1.5 mL/hr